British Works. 283 



showers, so destructive to vineyards and every other kind of rural crop through- 

 out Central Europe, changes what would be otherwise a violent storm into a 

 gentle shower. But a very small amount of demonstrative truth has been 

 added to the science of electricity since the time of Franklin, nearly eighty 

 years ago. 



" In treating of the phenomena of the electricity of the atmosphere, we must 

 premise some remarks on the sources from which it is derived. All the nu- 

 merous causes of excitation which are constantly in action on the surface of 

 the earth may be said to be sources of more or less of the electricity of the at- 

 mosphere. But, as it has been ascertained that one kind predominates greatly, 

 we must look for some origin to which both of these circumstances may be 

 ascribed. The intimate connexion which subsists between the formation of 

 clouds and the developement of electricity naturally leads to the supposition 

 of the electricity being dependent upon the vaporous portion of the atmo- 

 sphere, which is itself liable to similar variations. 



" The earlier electricians thought that the vapour necessarily acquired a pe- 

 culiar electric state in rising from a solid or liquid ; but Pouillet, who has re- 

 cently investigated this theory with remarkable skill, has demonstrated that the 

 conversion of pure water into vapour, at any temperature, is not attended with 

 any disturbance of the electric equilibrium ; but that vapour, rising from so- 

 lutions however weak, gives signs of electricity, varying in kind according to 

 the nature of the substance dissolved. From alkaline solutions the vapour 

 rises with the signs of — electricity ; from saline or acid solutions the vapour 

 carries up a charge of + electricity, and leaves the solution in a state of — 

 electricity ; and the rule was verified, particularly with regard to solutions of 

 sea salt. It cannot be doubted, therefore, that evaporation from the surface 

 of the sea forms a copious source of atmospheric electricity; and, as no natu- 

 ral collection of water is absolutely pure, lakes and rivers, and the humid soil, 

 roust add to it. 



" Besides this important modification of the former theory, Pouillet has, by 

 his ingenious and able researches, discovered an unsuspected source. When 

 gaseous bodies unite with each other, or a gaseous body with a solid, one of 

 the uniting bodies always gives out -f- electricity, and the other — electricity. 

 In the combustion of carbon, hydrogen, oils, &c, the carbonic acid formed by 

 the combination with oxygen is in a state of -f- electricity, and the unconsumed 

 portion remaining is in the opposite state. As plants, during vegetation, ex- 

 ert a chemical action on the atmosphere, sometimes converting its oxygen into 

 carbonic acid gas, and at others decomposing the carbonic acid already existing 

 in it, assimilating the carbon, and disengaging the oxygen, it was conceived that 

 electricity might be thus developed ; and, from the very extensive operation of 

 vegetation, the quantity might be sufficient to influence the atmosphere. The 

 results of experiments confirm this anticipation. When seeds were sown in 

 the earth there were signs of electricity as soon as the germs appeared on the 

 surface ; and the electricity became more evident as vegetation advanced. So 

 considerable was the evolution, that it was calculated that a powerful battery 

 might be charged by the vegetation from an area of one hundred square yards. 

 Every green tree and every tuft of verdure is, therefore, continually supplying 

 the atmosphere with electricity; and in hot humid climates, as that of Brazil, 

 the quantit}' derived from this source must be extraordinary, if we reflect on 

 the vigour with which the growth of the plants is carried on. According to 

 the assertion of a respectable traveller, rain in the evening will by sunrise have 

 given a greenish tinge to the earth; if the rain continue, there will be sprouts of 

 grass an inch long on the second day ; and on the third day the grass will be 

 strong enough for the pasturing of cattle. 



" The great sources of atmospherical electricity are, therefore, evaporation 

 chiefly, and vegetation ; the others to be noticed are comparatively insignifi- 

 cant, and, perhaps, do not coincide in contributing electricity of the same kind. 



" The exhalations from the flowers of plants differ in chemical constitution 

 from those of the green parts, and their formation in the corolla must be 



